Box goes through walls

So I've been trying to make a box follow the cursor and collide with objects but I've run into an issue I cant figure out... In this script Everything works fine except that when The box that it is attached to collides its stops, but once it has stopped when i move my cursor farther away it starts to teleport into and eventually past the other box it was collided with... Any ideas?

Here is the script:

using UnityEngine; using System.Collections;

public class CursorController : MonoBehaviour {

 private Vector3 cursorPos;
 private Rigidbody body;
 public float speed = 10f;
 public float slow = 1f;
 public float rate = 5f;

 // Use this for initialization
 void Start () {
     body = gameObject.GetComponent<Rigidbody> ();
 }
 
 // Update is called once per frame
 void Update () {
     cursorPos = Camera.main.ScreenToWorldPoint(Input.mousePosition);
     cursorPos.z = 10f;
     //transform.position = Vector3.MoveTowards(transform.position, cursorPos, speed);
     body.AddForce((cursorPos - transform.position) * speed);
     body.velocity = body.velocity/slow;
     slow = Vector3.Distance (transform.position, cursorPos) / rate;
 }

}